Conventional injection tools for performing injection-molding methods comprise a nozzle needle which is adjustable in the axial direction in order to control the injection process. Conventional needle-closing systems are driven pneumatically, hydraulically, mechanically or electrically. In this process, the needle is movable between a first end position (open) and a second end position (closed).
In order to control the injection quantity and the speed of the material flow, it is known to arrange the first end position in an adjustable way in order to reduce the opening cross section in the region of the needle tip in a selective way. A constant product quality can be ensured in this manner in an injection tool with a plurality of cavities because as a result of inevitable temperature differences, surface conditions, different distributor channels and the like, even when the injection tool is arranged in a careful way, it is not possible to avoid differing flow conditions during the inflow of the material. These irregularities can be compensated by setting the opening position of the nozzle needle, so that the quality of the produced end products can be ensured. It is known to set the end position of the nozzle needle mechanically, which is only possible however with an interruption of the production process. The setting process is respectively complex and leads to a reduction in the production capacity as a result of the interruptions in production. Furthermore, there is always the likelihood of the production of rejects after a standstill of the injection tool.
In order to avoid these disadvantages, mechanical systems are known which enable the setting of the flow cross-section in a tool with several cavities. As a result of the complexity of these apparatuses, they are limited to tools with a relatively low number of cavities, which furthermore need to have an adjusted arrangement (linear) in order to take the requirements of the adjusting device into account.
AT 5 750 U discloses an injection nozzle in which mechanical adjustability of the nozzle needle is provided. In this specification, the production process needs to be interrupted repeatedly in order to adjust the opening stroke. In this respect, the nozzle needle of the injection nozzle is arranged as a rigid connection between the piston of the nozzle needle and the stop screw.
DE 40 32 500 A1 describes an injection-molding device in which the digitally controlled stop piston and receiving piston of the injection nozzle are in connection with one another. This apparatus has a complex configuration and is susceptible to malfunctions.
EP 1 961 549 A1 discloses a needle actuating apparatus, in which embodiments of the piston are described among other things with which the nozzle needle is connected. The piston with which the nozzle needle is connected can be driven electrically, which is respectively complex.
U.S. Pat. No. 5,078,589 A discloses an injection apparatus in which the nozzle needle is connected to a locking screw.